Organic recycling with metal addition

Abstract

The invention is directed to methods for producing a granular nitrogen fertilizer from an organic material comprising adding a metallic salt to said organic material to form a slurry. Preferably the organic material comprises dewatered biosolids and contains water from a scrubber. Metallic salts that can be used comprise a salt of iron, zinc, or a mixture thereof. Preferred iron salts comprises ferric sulfate or ferric oxide, and preferred zinc salts comprises zinc sulfate or zinc oxide. Preferably, the metallic salt is mixed with an acid such as sulfuric acid to form an acidified metal salt. Slurry pH ranges from approximately 2-2.5. The acidified metal salt is added to the organic material in sufficient quantity to lower viscosity of the slurry such that the resulting fluid does not hinder fluid flow during operation. When the metallic salt comprises acidified ferric sulfate or ferrous sulfate, sufficient iron can be present to produce a fertilizer product with 0.1 weight percent to 10 weight percent iron sulfate calculated on a dry weight basis. The invention is also directed to fertilizer products made by the methods of the invention. Preferred products are granules and the metallic salt increases product hardness. Fertilizer granules preferably contain metal that is bioavailable to a plant when used as a fertilizer. Solubility of the metal of the product in water is enhanced, and the product is low staining.

Description

BACKGROUND 1. Field of the Invention This invention is directed to systems, devices and methods for converting organic material into fertilizer. More specifically, the invention relates to adding iron sulfate or other metallic salts to organic material prior to producing fertilizer from the organic material. 2. Description of the Background The disposal of sewage sludge is a significant world-wide problem. Current methods of disposing of sewage sludge include incineration, direct land or ocean application, heating and drying the sludge for sterilization and then applying it to land, depositing it in a landfill, or granulating the sludge with a standard rotary granulator with heating and drying being provided by exogenous heat sources (e.g. by burning purchased fuel). While some of these methods result in a fertilizer, such fertilizers are of relatively low analysis with regard to their plant nutrient value. Methods of expressing a fertilizer's plant nutrient value involve ident...

AI Technical Summary

Benefits of technology

One embodiment of the invention is directed to methods for producing a granular nitrogen fertilizer from an organic material comprising adding a metallic salt to said organic material to form a slurry. Preferably the organic material comprises dewatered biosolids and contains water from a scrubber. Metallic salts that can be used comprise a salt of iron, zinc, or a mixture thereof. Preferred iron salts comprises ferric sulfate or ferric oxide, and preferred zinc salts comprises zinc sulfate or zinc oxide. Preferably, the metallic salt is mixed with an acid such as sulfuric acid to form an acidified metal salt. Slurry pH ranges from approximately 2-2.5. The acidified metal salt is added to the organic material in sufficient quantity to lower viscosity of the slurry such that the resulting fluid does not hinder fluid flow during operation. When the metallic salt comprises acidified ferric sulfate or ferrous sulfate, sufficient iron can be present to produce a fertilizer product with 0.1 weight percent to 10 weight percent iron sulfate calculated on a dry weight basis. When sulfuric acid is added to the organic material, it is preferably added prior to reaching a mix tank and at a rate of approximately 1.75 percent of a total feed rate to result in a pH range of 3.0 to 3.5.

Preferably the slurry is pumped into a shear mix tank that contains a high shear rotary agitator which turns at a speed sufficient to produce high shear. Slurry is passed from said shear mix tank to a holding or equilibrium tank containing an agitator. The agitator may provide approximately 2 hours or more of storage for the slurry. Holding or equilibrium tanks can be operated to maintain a pH of 3.0 to 4.0 with a solids content of between 15 percent and 28 percent solids. Metallic salt may chemically bonds with one or more elements of the slurry. When using an iron salt, the iron can bond with ammonium sulfate or ammonium phosphate present in the slurry. This can enhance granulation formation, and reduce sulfur compounds in the slurry, and odor and dust formation during operation.

Preferably the metallic salt initiates chemical hydrolysis of organic molecules in the slurry. This can drive sulfur compounds out of the organic material reducing odorant sources in a resulting fertilizer product.

Preferably the metallic salt is added to the organic material in a pipe-cross reactor or a tubular reactor. The metallic salt enhances reaction kinetics of the pipe-cross reactor and lowers viscosity of the slurry such that operation of the pipe-cross reactor is more controllable that without the metallic salt.

Another embodiment of the invention is directed to fertilizer products made by the methods of the invention. Preferred products are granules and the metallic salt increases product hardness. Product may have a crush weight of greater than 6 pounds or preferably greater than 7 pounds. Granules of fertilizer preferably contain metal that is bioavailable to a plant when used as a fertilizer. Solubility of the metal of the product in water is enhanced, and the product is low staining.

Problems solved by technology

The disposal of sewage sludge is a significant world-wide problem.

While some of these methods result in a fertilizer, such fertilizers are of relatively low analysis with regard to their plant nutrient value.

However, the use of a preneutralizer poses various disadvantages including difficulty in obtaining accurate control of flow rates.

Additionally, operating and equipment costs associated with the use of a preneutralizer often represent a significant expense.

One potential drawback of exothermically treating relatively low analysis organic waste material with reactors, such as a pipe cross reactor or tubular reactor, is the potential for exhausting noxious odors during the process.

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